This is a cheap 'no brand' 20A ESC.
It works as well as any but just look at the impression the MOSFETS have made of the conductive layer of the heat sink.
Two of the MOSFETs don't really make any contact at all and it is only partial on 2 more!
There must be a real risk it would fail due to overheating no matter how much airflow actually passed over the heat sink.

It needs a thicker and softer conductive layer on the heat sink to ensure each MOSFET is adequately cooled.